Can we use verb 'build' and phrasal verb 'build on' interchangeably? For example - I have to build /build on my credit rating for becoming eligible for a home loan. Will it (interchangeability of verb and phrasal verb) applicable to following verb also? "decide and decide on"
Build X can lean towards meaning X doesn't exist yet and you are going to construct X.
Build on X means you are doing new things to enhance or evolve X.
Build up X can phrasally mean "obtain a supply of X for later."
The on in decide on isn't really a phrasal variation. On X can be used if X is a topic/purpose/point of a conversation, meeting, etc.