Is there any opposite of "Ground up" phrase? Something like "Top-down : Bottom-up"
The phrase from the ground up generally means completely or starting from scratch, as in this definition.
When a task is not approached from the ground up, it is being done incrementally, or perhaps superficially. If you wish to convey that the actor is not paying attention to basics or fundamentals, you could say his head is in the clouds or he is living in an ivory tower.
I agree partly with bib that we're looking for an opposite to starting from scratch rather than a literally physically opposite metaphor.
Another way to consider this opposite is to think of someone participating after completion, so maybe after the fact would work?
Or, if you're taking the not from the start approach, think incremental change of something substantial, such as standing on the shoulders of ... or organic improvement?