I do not believe I can trust mobile devices: between the opaque development practices of "open source" Android, the outright hostility of iOS to inspection by developers, and the enormity and quality of baseband radio firmware, it is frankly always a better idea to install no app than just trying to pick the least untrustworthy one.
"What do you trust more than Signal?" presupposes that I must trust _something_. I mustn't.
"I appreciate SDF but it's a general-purpose server and the name doesn't make it obvious that it's about art." - Eugen Rochko