Tea scale possibly is to increase by stages (8)
I believe the answer is:
escalate
'increase by stages' is the definition.
'escalate' can be an answer for 'increase' (escalating is a kind of increasing). I'm not sure about the 'by stages' bit.
'tea scale possibly' is the wordplay.
'possibly' is an anagram indicator.
'tea'+'scale'='teascale'
'teascale' is an anagram of 'ESCALATE'.
'is to' is the link.
Can you help me to learn more?
(Other definitions for escalate that I've seen before include "get high" , "Increase in magnitude" , "Magnify" , "Raise to higher level, perhaps war" , "mount in tension" .)