Any small starter amp would work for your intended use, unless you need battery power.
Will you be unable to travel to a music store with your new bass to try some out?
Good idea! I'll get the U-Bass on mail-order (no local stores hold them) and then take it along to the local store to try out the amps! Why didn't I think of that?! Thanks Dave.
I'm sure that for twice the price, the Phil Jones is much more than twice the amp compared to the Roland.
But, I play regularly with two U-Bassists who bring their Roland micros to small acoustic uke circles, and they sound great in that setting.
No problem being heard with half a dozen ukes and voices, banjo uke and harmonica, when nothing else is amplified.
The battery power let's us play outdoors with U-Bass. The drum machine is fun.
But yes, they're only 5 watts, so a 70 watt pro amp like the Phil Jones, or any 20-50 watt conventional combo bass amp will blow one away in a big room, at higher volumes where other players use amps, with a drummer, etc.
Good luck, welcome to the wonderful world of bass ukulele.