"that I can see" must be a clause, not a phrase, since there is a subject and a verb. "All" is a pronoun, so the clause is a relative clause.
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Eddie88How come 'all that I can see' is a noun phrase and not a noun clause?A noun clause is a clause that acts as a noun. The clause part of all that I can see is that I can see, not including all. And that I can see is a relative clause, which means it acts like an adjective, not a noun. So the whole group all that I can s