Live as if Already Resurrected
In Romans chapter 6, Paul is making an argument against continuing to live in sin (vv.1-2).
He advances that argument by showing that in choosing to be "baptized into Christ Jesus" (v.3a, NKJV), a believer has publicly identified with Christ's death for them (v.3b). Then he states that even as a believer has identified with Christ's death, they ought also to identify similarly to Christ's resurrection, that is "walk in newness of life" (v.4).
In short, Paul is saying in vv.3-4 that a believer ought to be walking as if already resurrected. This plays out in more detail up to verse 14 (including v.11).
He continues his point by acknowledging in v.5 that the baptismal identification with Christ's death means believers have been "united" (σύμφυτοι, nominative plural, "identified with"
1) "together in the likeness of His death," that is the ὁμοιώματι (dative singular of ὁμοίωμα; "likeness," i.e. similar experience or form
2). So like the identification with Christ's death, believers will "certainly" be so "of resurrection" as well.
The Greek here uses the strong additional ἀλλὰ (often translated "but," yet when showing a strong alternative or addition, "yet, certainly, at least"
3) combined with the additive use of καί (so here, "also"
4). The Greek also elides words before "of resurrection," since it expects the prior statement to supply the idea (hence the NKJV italicized text, "certainly we also shall be in the likeness of His resurrection"). This elision adds even more strength to the parallel, since one has to go back to the "in the likeness" before "of His death," which makes that wording function for both parts of the parallel.
So v.5 sets up the parallel, like death = like resurrection.
Then vv.6-7 expands further on the death picture. A believer, in identifying with the death, has identified with Christ's crucifixion because of (and to overcome) sin, which overcoming actually/finally occurs at one's actual death, when "the body of sin might be done away with" (v.6b), for sin dwells in the flesh and so that flesh must die (or be changed from what it is) to deal with sin (compare Rom 7:25, 8:3, and here in context Rom 6:7). But just as the death in actuality will deal with the sin in the flesh, in fact "do away" with it, even now, having identified with that death, believers "should no longer be slaves of sin" (v.6c). Why? Because those identifying with the death ought to identify with the freedom from sin that such death will bring (v.7).
So vv.6-7 advance that since death actually frees one from the sinful flesh, having identified with Christ in death, a believer ought to walk as if sin free now.
Then further, v.8 picks up the parallel to the resurrection again, that if the identification to death has been made, then believers ought to also believe there is coming a time they will live with Christ. When? In the resurrection, as He has been raised from the dead (compare 1 Cor 15:12ff), and will die no more (v.9).
How does Christ live in this resurrected state? Having died "to sin" (v.10a), He now "lives to God" (v.10b). That's not to say He was not living to God before, during His incarnation here on earth, but now He lives in a new way where sin has no bearing on His actions (He already dealt with sin in that He died for it).
So "likewise" believers should live as if sin has no bearing or power in their lives (v.11a), and instead should "reckon" (the present, middle/passive form of λογίζομαι), that is, "account" or "consider"
5 themselves "to be dead indeed to sin, but alive to God in Christ Jesus our Lord" (v.11b-c). This is the same accounting term used of how God accounts a believer righteous through faith (bolded words are λογίζομαι), Romans 4:3-8 (NKJV)—
3 For what does the Scripture say? “Abraham believed God, and it was accounted to him for righteousness.” 4 Now to him who works, the wages are not counted as grace but as debt. 5 But to him who does not work but believes on Him who justifies the ungodly, his faith is accounted for righteousness, 6 just as David also describes the blessedness of the man to whom God imputes righteousness apart from works: 7 “Blessed are those whose lawless deeds are forgiven, And whose sins are covered; 8 Blessed is the man to whom the LORD shall not impute sin.” 9 Does this blessedness then come upon the circumcised only, or upon the uncircumcised also? For we say that faith was accounted to Abraham for righteousness. 10 How then was it accounted? While he was circumcised, or uncircumcised? Not while circumcised, but while uncircumcised. 11 And he received the sign of circumcision, a seal of the righteousness of the faith which he had while still uncircumcised, that he might be the father of all those who believe, though they are uncircumcised, that righteousness might be imputed to them also, 12 and the father of circumcision to those who not only are of the circumcision, but who also walk in the steps of the faith which our father Abraham had while still uncircumcised.
So Paul is flipping the imagery of chapter 4 of Romans. God now accounts believers righteous through their faith, though they are not yet actually righteous, just accounted so; that will change to reality at the resurrection, when they are "made righteous" (Rom 5:19), so the accounting is justified based on the future act of God for believers. Likewise, believers are now to account themselves dead to sin, and alive to God (like Christ in His resurrected state is alive, sinless), though they are not yet actually dead to sin and resurrected like Christ, just to be considering themselves so in their conduct now; that will change to reality at the resurrection, when the new body is not corrupted by sin (1 Cor 15:52), so the accounting is justified based on the future act of God for believers.
The Answer to Your Direct Question
The resurrection is still viewed as yet to come, but believers identifying with Christ in His death are to walk now as if already raised to a new, sinless existence in the resurrection. The grounds for this "as if" accounting are in the fate accompli that is prophesied to come, the actual resurrection, demonstrated in Christ's already resurrected existence, and as good as fact in God's mind as the believers future righteousness is, and so ought to be as good as fact in the believers' minds.
Because of that accounting, the conclusion of the passage follows in vv.12-14 (bold added)—
12 Therefore do not let sin reign in your mortal body, that you should obey it in its lusts. 13 And do not present your members as instruments of unrighteousness to sin, but present yourselves to God as being alive from the dead, and your members as instruments of righteousness to God. 14 For sin shall not have dominion over you, for you are not under law but under grace.
Here Paul ties in the righteousness that God accounts believers as already having (though they do not), with the death to sin and new life to come that believers are to be accounting as also already having (though they do not), so that "sin shall not have dominion over you."
Regarding the Philippians 3 passage
I think it is clear that there is a relation to this passage: righteousness by faith discussed in v.9, Christ's resurrection and sufferings (death) and a "knowledge" and "fellowship" with those in v.10, attaining resurrection in v.11, yet not yet having attained the resurrection or perfection in v.12a, but needing to strive for that perfection despite failures vv.12b-14.
1 William Arndt, Frederick W. Danker, Walter Bauer, and F. Wilbur Gingrich. A Greek-English Lexicon of the New Testament and Other Early Christian Literature ( Chicago: University of Chicago Press, 2000), s.v. σύμφυτος. Here after referred to by the common abbreviation BDAG.
2BDAG, s.v. ὁμοίωμα.
3 BDAG, s.v. ἀλλά, #4a.
4 BDAG, s.v. καί, #2b.
5 BDAG, s.v. λογίζομαι.