Update documentation for phone account sort order

Update documentation to reflect that the sort order extra
should contain integers.

Bug: 169153499
Test: docs only
Change-Id: Ic5269d577f007e01a0c9eaa95cd7e8814ab8f79a
Merged-In: Ic5269d577f007e01a0c9eaa95cd7e8814ab8f79a
1 file changed