Rename phoneId to slotIndex

Rename phoneId to slotIndex. Some of the classes are being put in an API
surface and phoneId is an internal concept. slotIndex is its replacement
and should be identical.

Bug: 148403082
Test: treehugger build only
Change-Id: Iecbf347c9d13877f2e3f74b6daa22661bade257a
7 files changed