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[\[Phi], j]], {j, 1, 10}];
Cases[d, Subscript[__, __], {1, -1}]

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

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]}

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

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[\[Phi], j]], {j, 1, 10}];
Cases[d, Subscript[__, __], {1, -1}]

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