If you want one, I'm sure a search on the Play store (or whatever Apple uses) will find several.
But please note most phones wont measure above ~90 dB simply due to the way phone mics work. They are geared for normal voice conversation so simply don't need to register anything too loud. So if you are looking for something to measure sound levels from an exhaust, for example, there aren't any. At least none that anyone who needs to trust one trusts (like track officials, or the police, for example).
If you want to measure your sound levels I would suggest getting something akin to
this (<-- That's a link).