Migrate phone account sorting to use lamba expressions and add test.

Refactor the phone acconut sorting code to use lamba expressions and
to ensure sorting happens anytime phone accounts are written (rather than
just when they're added/edited).

Test: Unit
Bug: 34872161
Merged-In: I3b398a3ee004425947def808bf187003ff82ccf2
Change-Id: I3b398a3ee004425947def808bf187003ff82ccf2