flist = {ph, ar, x, y};
The most straightforward approach is the one suggested by @Bob Hanlon in the comments section: Plot[Tooltip[#@l, #] & /@ flist, {l, 0, lmax}, Evaluated -> True].
The following unusual usage of the option PlotStyle also gives the desired result:
Plot[Through@flist@l, {l, 0, lmax}, Evaluated -> True, Filling -> Axis,
PlotStyle -> (Function[t, Tooltip[#, t] &] /@ flist)]
You can also add tooltips via post-processing:
Block[{j = 1}, Plot[Through@flist@l, {l, 0, lmax}, Evaluated -> True, Filling -> Axis] /.
Line[x_] :> Tooltip[Line[x], flist[[j++]]]]
(* same picture *)