1.
If you ~ something or if it builds up, it gradually becomes bigger, for example because more is added to it.
The regime built up the largest army in Africa...
Slowly a thick layer of fat builds up on the pan’s surface.
PHRASAL VERB: V P n (not pron), V P, also V n P, V P to n
2.
If you build someone up, you help them to feel stronger or more confident, especially when they have had a bad experience or have been ill.
Build her up with kindness and a sympathetic ear...
PHRASAL VERB: V n P
3.
If you build someone or something up, you make them seem important or exciting, for example by talking about them a lot.
The media will report on it and the tabloids will build it up...
Historians built him up as the champion of parliament...
PHRASAL VERB: V n P, V n P as n/-ing
4.
see also build 6, 8, build-up , built-up