I can't translate the greek, but I can tell you that the answer comes from the wider context:
19 I hope in the Lord Jesus to send Timothy to you soon, so that I too may be cheered by news of you. 20 For I have no one like him, who will be genuinely concerned for your welfare. 21 For they all seek their own interests, not those of Jesus Christ. 22 But you know Timothy's proven worth, how as a son with a father he has served with me in the gospel. 23 I hope therefore to send him just as soon as I see how it will go with me, 24 and I trust in the Lord that shortly I myself will come also. 25 I have thought it necessary to send to you Epaphroditus my brother and fellow worker and fellow soldier, and your messenger and minister to my need, 26 for he has been longing for you all and has been distressed because you heard that he was ill. 27 Indeed he was ill, near to death. But God had mercy on him, and not only on him but on me also, lest I should have sorrow upon sorrow. 28 I am the more eager to send him, therefore, that you may rejoice at seeing him again, and that I may be less anxious. 29 So receive him in the Lord with all joy, and honor such men, 30 for he nearly died for the work of Christ, risking his life to complete what was lacking in your service to me. - Philippians 2:19-30 ESV (emphasis added)
To summarise: Paul expresses the hope that he will send Timothy (to the Philippian church) soon because he, of all his co-labourers, was the most equipped to care for them and build them up in the gospel. In view of the wider context, we can interpolate a 'But' at the beginning of v25 as he explains why he is sending Epaphroditus instead of Timothy. The key phrase to explain this is the second half of v26 "[he] has been distressed because you heard that he was ill." The Philippians will be anxious because they've heard of Epaphroditus' condition - additionally the anxiety would be greatly heightened if/when they learn of the near-mortality of Epaphroditus' condition. Epaphroditus is anxious because as long as he is apart from the Philippians, they will have needless concern for him and their anxiety may very well be increasing as they receive (necessarily delayed by the speed of communication in the ancient world) dire reports of his condition. Paul is anxious because both Epaphroditus and the Philippians are anxious - which all goes to show that (particularly amongst a devoted community of love) anxiety can be a highly contagious condition! The solution is obvious: rather than what was the most likely original plan of Epaphroditus assuming Timothy's role of ministering to Paul's personal needs so Timothy can be released for the ministry of the Gospel, Epaphroditus will instead be sent back home to allay everybody's anxiety and Timothy will have to play gopher a little longer.
