Is it possible to filter a map report on the mobile version?

The mobile version is very limited at the moment.  With the new User Interface release of "Mercury" later this year, mobile filters will be added.

In the mean time, I'd recommend creating a report that asks the user for the "city" or whatever filtering criteria needed.

The filter would be something like;
Show "clients" where "city" is equal to "Ask the User"

Then they can just type in the city. 
You could add multiple "ask the user" options if they want more filtering options.