If it's a busy apartment building with other people coming and going a guy sitting in his car looking at his phone shouldn't be a big deal. If he's just wandering around he could look suspicious like maybe he's looking for a car to break into. I think each provider and each client have their own expectations of how to behave pre-session. Unless it's unreasonable just do what the provider feels comfortable with and it shouldn't be that big of an issue.
This is just one more reason why I prefer to see a regular provider. You both know what to expect from each other and things like this are rarely a problem.