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I'm working on a project our site - building links for iPhone Repair.

For the term "iphone repair miami" - is it more ideal to link to the root domain (xxx.com) or to the subpage that is about iPhone Repair (xxx.com/iphone-repair)?

I would imagine the latter - but obviously that page has less authority than the root.

Thanks!

It's certainly on a case-by-case basis as I've seen. Certain terms (ex. photographers) is searched much more as a plural than as singular. The real answer to this question is do your keyword research, and see which terms is more sought after.