Can prepositional phrases that aren't relitive be treated as such?

For example, "He ran up the stairs of his basement apartment in the slums." In that sentence, 'in the slumbs' is nonrelitive because he only has one apartment. Does the relitive/nonrelitive rule apply to prepositional phrases?
relative. I fixed it in the header.

I don't fully understand what you're asking.

Prepositional phrases are not classified as relative or nonrelative.

Maybe you're thinking of restrictive relative clauses and non-restrictive relative clauses?

Yeah, that's what I was thinking of. Htanks