So , there are phone apps which i can download, have a lightning network wallet with my own keys?
Discussion
Phoenix wallet is the only which i know that keep your private key
Basically i will have a lighting node in my smartphone?
Phoenix is a lightning node, however is restricted by the developers to connect only with the ACINQ node.
Its the most free lightning wallet for smartphone right now, but some of the services its offer are not "trustless" yet ( for receive new channels towards you, you must trust the developers for example)
Maybe the solution is actually building your own lighting network node
start9 vs umbrel ?
Its a solution, with some drawbacks: your wallet will be less portable.
About Start9 and Umbrel, i don't have enough information for give a valuable opinion. I will suggest to use the one who provide more documentation and troubleshooting knowledge