How can I force iPhone to resync contacts from server?
Maybe you've already tried this but I'll suggest it anyway.
Check Groups

Open Contacts
Tap the arrow in the upper-left corner labelled Groups if it exists.
Ensure you have selected the right group of contacts.

Try Re-Sync
If you need to re-sync because the above did not work you could try this:

Open the Settings app
Open Accounts &amp; Passwords (or the Mail section on older iOS).
Select the account causing problems. (Usually called Exchange.)
Turn Contacts off and tap ‘Delete From My iPhone’ when prompted.
Turn Contacts back on and tap ‘Sync’ when prompted.