Phone: Add summary to block private numbers functionality

This commit adds a summary text to the block private numbers
functionality to avoid ugly ellipsizes in languages where the
translations get longer (e.g. German).

Change-Id: Ie57cb2a41ec6689855c1d6879f66f439bb9e8b7a
Signed-off-by: ChampionSwimmer <android@championswimmer.tk>