We know that a clause is a sentence which is a part of a sentence. So, a clause is itself a sentence having a subject and a predicate, but a phrase is just a group of words. To tell you the truth,I was terrified. He regrets now having jumped. I apologized for being late. Nowadays Infinitives, participles and gerunds are regarded as 'non-finite clauses'.
My question is : - (1) Are all the three parts (written above in bold letters) phrases as well as (non-finite) clauses at the same time? (2) Why are they regarded as clauses though they are not a complete sentence having a subject and a predicate? (3) Is there no distinction between a phrase and a (non-finite) clause in this case?