Is it ok if I pass through a RJ11 (Phone line) cable outside and leave it while it is raining?
RJ11 is actually the name of the connector specification. 

Wire/insulation and cable jacket materials vary for the specific purpose.  Phone wire may also need to be thicker (e.g., lower gauge than Cat 5e) for longer runs, to avoid excessive voltage drop, depending upon your system.

There are phone cables specifically intended for outdoor use, providing better sun and water protection.  It could then be wired to a properly protected RJ11 receptacle, also designed for outdoor use.  I would not recommend using unapproved electrical wiring outdoors - even for phones. The phone company typically puts somewhere between 50 to 150 volts AC down that wire to make the phone ring.