Login to Switch, check on what vlan the phone mac has been learnt on.
use the show mac address-table
Check column 1.
What is the phone model ? We've had similar issues, usually unplugging/ plugging works.
Check phone IP . Usually it takes IP from the voice vlan,
But at times, it does take the IP from the data vlan & now the pc doesn't have a source from which it can request
( Sorry, technically not so strong to explain)