Variables[Level[expression, {-1}]]

you have to know that Subscript variables is not considered as pure variables in MMA. it is basically a built in function expression. in this case I would suggest you to used:

    d = Table[Exp[Subscript[ϕ, j]], {j, 1, 10}];
    Cases[d, Subscript[__, __], {1, -1}]

    {Subscript[ϕ, 1], Subscript[ϕ, 2], Subscript[ϕ, 3], \
    Subscript[ϕ, 4], Subscript[ϕ, 5], Subscript[ϕ, 6], \
    Subscript[ϕ, 7], Subscript[ϕ, 8], Subscript[ϕ, 9], \
    Subscript[ϕ, 10]}