ἀφθαρσία (aphtharsia) occurs 8 times in the NT: Rom 2:7, 1 Cor 15:42, 50, 53, 54, Eph 6:24, 2 Tim 1:10, Titus 2:7.
BDAG defines this as "the state of not being subject to decay/dissolution/interruption, incorruptibility, immortality" Thus, I would argue that "incorruption" or "imperishable" would be a better word in Rom 2:7 as there are other words that specifically mean immortal in the Greek, eg, ἀθανασία (athanasia) which is used in apposition to imperishable in 1 Cor 15:54.
Rom 2:7 is written in quintessentially Pauline terse rhetoric. Here is my (overly) literal translation:
To those [who] indeed with endurance of good work, glory and honour
and imperishability are seeking, life eternal.
Most version supply "are given" before "life eternal" (there are some important exceptions). This is quite understandable but not completely defensible. If we take the next verse together, we can then find a simple contrast (my translation):
- V7: to those who by endurance of good work seek for glory, honor, and incorruptibility, eternal life;
- V8: but to those who are self-seeking, and disobeying the truth, but obey unrighteousness, wrath and anger.
Here "incorruptibility" refers to the spiritual body that we get at the resurrection (1 Cor 15:40-54) that is the means by which we achieve immortality with Christ as the source of life (1 John 5:11, 12).
ζωή (zóé) as used in Rom 2:7, according to BDAG means, "transcendental life", that is, the life to come following the resurrection of the saints. Thus it is used with the adjective "eternal" or "everlasting" in John 3:15, 36, 4:14, 5:24, 39, 6:27, 40, 47, 54, 68, 10:28, 12:25, 50, 17:2, 1 John 1:2, 2:25, 3:15, 5:11, 13, 20, etc.
Thus, the two lists in Rom 2:7, 8, one applying to the righteous and other to the wicked, can be seen as opposites of each other with the last item in each list the final destiny. Some versions insert words (eg a verb, "are given") to emphasise this idea.