|Dear Rick ,|
RJ11 plug does in fact fit into RJ45 jack. As long as you use pair #1 (blue - white/blue) for the phone line connection, the center pins of RJ11 and RJ45 will be in contact and everything will be fine.
There have been problems reported with mediocre quality RJ11 plugs damaging RJ45 outermost pins, so I would advise you to check your plugs first. Just plug it in, then out and observe the RJ45's pins #1 and #8. If they are OK, you can use your RJ11s in any RJ45 jack.
Dmitri Abaimov, RCDD