Gordon Fee on Title - "Saviour".

"This (Philippians) is the first and only time in the Church corpus that the title "Saviour" appears (3:20). In this case since it occurs in the context of "citizenship" it almost certainly stands in direct confrontation with the Emperor Nero who is acclaimed throughout the empire as "Lord and Saviour ...

Significantly for both his readers context and for our understanding of Paul's christology, the One who we "eagerly await" is first of all designated "Saviour". The significance of this is highlighted by it's rarity in Paul's writings - only once heretofore (Ephesians 5:23) has he used this appellation of Christ and in that case it was not fully titular".

Gordon D Fee - "Pauline Christology - An Exegetical/Theological Study" - Hendrikson (2007) - (pp371, 402).