After running Synchronization, changes made in to an address or phone number are reverted to old information. This occurs when the address or contact type is the same in both systems.
If a phone number is updated in one database and then updated in the other before synchronization is run, the information from the phone number updated last will overwrite the phone number in the other database.
Set up synchronization to run as a scheduled task every 15 minutes. This will decrease the likelihood of changes being made to the same records during the same timeframe.