Depends on the line, and the router, but technically, yes.
You divide the existing speed between the two, so neither will likely work like you expect. The result is less than half.
I am assuming you mean DSL since you are talking about a phone line, and the DSL connection will be the problem. DSL change will be detected and stopped by your IP provider. They are not dumb. Their detection equipment is designed to prevent this... and your agreement with them specifically prohibits it in every market I have seen. So you risk having no connection, and perhaps putting yourself at legal risk.