I assume that Φ mentioned in your question is the null set.
An element of the set is one of the things in the set.The empty set is not an element of (1,2,(3,4),5).
Instead it is the set that doesn't not contain any elements
Null set is a subset of every set.
The notation (Φ) becomes different.It is a set that contains an empty set. But still it doesn't contain any element.. So it is also a subset.