How do I identify "infinitive clauses/phrases" and "subjects"?

There is no clause in the sentences. The first infinitives in both sentences are adjectival which cannot be separated from the noun phrases which begin the two sentences to form the subjects of to be verbs is and is respectively. The second elements after to be verbs are infinitive phrases which perform the functions as the complements to the subjects. There is no clause among the infinitives because there is no finite verb in them all.

From Idoko, Ejike Celestine (Celestial Academic Centre)

Modern grammarians consider such constructions clauses, not phrases. What traditional grammarians called infinitive phrases are now called infinitival clauses, a type of nonfinite clause.