Sometimes you will get a situation when contact cards in Lync client showing wrong phone numbers.
This is because of this menu in Lync client:
No matter of source issue, you must have a tool to investigate what happening in Lync SQL database (as soon as initial data for building Address Book files located there).
From this moment we will be talking about RTC database in RTCLOCAL instance that is located on Front-End server (in Enterprise deployment). Remember that in Enterprise Deployment every specific user can rely on their own "primary" server. If you have Standard deployment - there will be no problems to indentify the server needed.