Brian has forwards an outline of the epistle that was published many years ago by C H Welch.
A 1:1,2 SALUTATION
B 1:3-26 FELLOWSHIP IN GOSPEL from FIRST DAY
C 1:27-2:5 STAND FAST. MIND OF CHRIST.
D 2:6-11 The SEVENFOLD HUMILIATION of CHRIST. EXAMPLE.
E 2:12-17 EXHORTATION to WORK OUT YOUR SALVATION
F 2:17-30 EXAMPLE of PAUL, TIMOTHY and EPAPHRODITUS
E’ 3:1-3 EXHORTATION to BEWARE
D’ 3:4-19 The SEVENFOLD LOSS of PAUL. EXAMPLE
C’ 3:20-4:10 STAND FAST. BODY of GLORY.
B’ 4:11-20 FELLOWSHIP in BEGINNING of GOSPEL
A’ 4:21-23 SALUTATION CAESAR’S HOUSEHOLD.
Note: I found a similar proposal by A. Boyd Luter and Michelle V. Lee (1995). Philippians as Chiasmus: Key to the Structure, Unity and Theme Questions. New Testament Studies, 41, pp 89-101 doi:10.1017/S0028688500022967.
A CHIASTIC OUTLINE OF PHILIPPIANS
(1.1-2) Opening Greetings: Previewing ‘Partnership’ Theme, Emphasizing Servant-Leadership.
A. (1.3-11) Prologue: ‘Partnership in the Gospel’ Theme Introduced with Prayerful Gratitude.
B. (1.12-26) ComfortIExample: Paul’s Safety and Right Think- ing in the Midst of a Difficult ‘Guarded’ Situation.
C. (1.27-2.4) Challenge: Stand Fast and Be United, Ful- filling Paul’s Joy!
D. (2.5-16) Example /Action: Christ’s Example of Humility and Suffering before Glory, then Related Behavioural Instructions.
E. (2.17-3.1a) Midpoint: Caring Models of Gospel Partnership, Two of Which Are Sent to Help Immediately.
D’. (3.1b-21) Example IAction: Paul’s Example of Humbling and Suffering before ‘Upward Call’/ Transformation, then Instructions.
C (4.1-5) Challenge: Stand Fast and Accentuate Existing Joy by the Reconciliation of Two Past Gospel Partners!
B’. (4.6-9) ComfortIExample: The Philippians’ ‘Guarded’ Peace of Mind and Right Thinking in the Midst of an Anxious Situation.
A’. (4.10-20) Epilogue: Partnership from the Past Renewed, with Expressed Gratitude.
(4.21-3) Closing Greetings: Reviewing Partnership Theme, Emphasizing Oneness of the Saints.
Note: I also came across deep skepticism about large scale chiasmus in Stanley E. Porter and Jeffrey T. Reed (1998). Philippians as a Macro-Chiasm and its Exegetical Significance. New Testament Studies, 44, pp 213-231 doi:10.1017/ S0028688500016489