There seems to be a bug in the Lync update KB 2863908 that breaks integration between Outlook 2010 and Lync 2013.

If you search for a local outlook contact in lync, it will not display a phone number  on the contact card unless you remove the email address from the contact. If an email address is present on the contact, the lync client will not display any phone numbers for the contact.

As far as I have seen it only occurs when you have Lync 2013 and Outlook 2010.

Removing KB 2863908 resolves the issue.

There are also a couple of threads on the technet forums about this:

http://social.technet.microsoft.com/Forums/en-US/4317ec0e-3287-427d-b875-5b9c93997139/lync-client-2013-does-not-get-contact-phone-numbers-from-outlook-2010?forum=lyncprofile

http://social.technet.microsoft.com/Forums/lync/en-US/130ff6ff-54aa-42a2-86c5-69761eec446a/lync-2013-client-does-not-show-outlook-contact-numbers?forum=ocsclients