? power surge with inverter?

I'm a new camper owner and admittedly don't know alot of stuff yet.
We have what I was told is a power inverter installed on the floor of our camper under a cabinet.
I tried using it to charge my phone (the gen was running; I think the gen needs to run for the inverter to work?)
The phone continuously turned on and off, so the power was not being supplied consistently.

Please can someone tell me how this is supposed to work? I havent tried running a vaccum cleaner or anything from it yet...
thanks