You dont need to move a license from one phone to another.  Phones are configured within CUCM based on the number of DLU's availble to you.  Each phone type consumes a certain number of DLU's.  For ex:, 794X and 796X phones consume 4 DLU.  When you do CUWL licensing, Pro and Std provide a certain number of DLU loaded per each type of user (dont recall actual numbers here but let's say Std gives you 14 DLU).  In the licensing portion of CUCM, it will display how many DLU's you are licensed for and how many are used/remaining.

Hailey