Start by powering off the dsl, and the router. power up the dsl first, and give it a minute them power up the router. Recheck speeds on the computer.
Do your phones have wifi (they should if you are using them as a hotspot)?
If they do go to a speedtest website, and test the speed in the same room as the router, outside near the wall, outside your RV on the side that has the router, inside the door of the rv, and next to the computer's wifi antenna (have the computer off for the tests). The speeds should be fastest at the router, and drop as you move away. If they drastically drop as you go inside the rv then a repeater with an inside and outside antenna will help, if they are about the same inside or out you may need to replace the router.
If either the router or computer (or both) have external antennas that are removable, you can replace one or both with high gain antennas - again if the speed is about the same no matter where you are in the room with the router or outside the router may be bad. Another option is (not cheap) buy 100' of cat5 cable, and plug the DSL modem directly into the computer - if the speeds are ok then it is not the dsl, it is something else.
