pool pump wiring size
You can't use interior wire (NM aka Romex) for outdoor, underground or outside conduit applications.  As an example if the cable contains that paper wadding, that's a big no-go.  You need UF cable if direct burying, or that or THWN-2/XHHW individual wires for conduit. 

#14 NM is generally white (rarely black). UF is gray. 

Voltage drop wise, that sounds fine.  You don't even need to think about voltage drop til at least 60' on a 120V circuit, and even then only if you are running at hard circuit limits (which you should not) and believe in 3% (which you should not). 

Given that you are well under 15A, and 3% isn't that important for a panel-final load run, you are fine.