I have heard/read that expression several times… somehow, the term “apostle” seems to comprehend only the Twelve Apostles… yet, it is not “Biblical” (a term on which non-Catholic Christians tend to base their arguments):
For I am the least of the apostles and do not even deserve to be called an apostle, because I persecuted the church of God. (1 Corinthians 15:9)
I have made a fool of myself, but you drove me to it. I ought to have been commended by you, for I am not in the least inferior to the “super-apostles,” even though I am nothing. (2 Corinthians 12:11)
5 and that he appeared to Cephas, and then to the Twelve. 6 After that, he appeared to more than five hundred of the brothers and sisters at the same time, most of whom are still living, though some have fallen asleep. 7 Then he appeared to James, then to all the apostles, 8 and last of all he appeared to me also, as to one abnormally born. (1 Corinthians 15:5-8)
In the above passages we have St. Paul: a) designate himself as an apostle, b) demonstrates that there are indeed ranks (at least from people’s perspectives–as it happens with today’s “super-evangelists/preachers”) amongst apostles to which he has been relegated to an inferior class, and c) he distinguishes between the Twelve and all of the apostles (which implicitly tells us that there are more than Twelve/Thirteen).
Clearly, Apostle is a specific title designating the Twelve or one of the Twelve:
•The name Apostle denotes principally one of the twelve disciples who, on a solemn occasion, were called by Christ to a special mission. In the Gospels, however, those disciples are often designated by the expressions of mathetai (the disciples) or dodeka (the Twelve) and, after the treason and death of Judas, even of hendeka (the Eleven). (newadvent.org/cathen/01626c.htm)
Yet, “apostle” was also a title given/used to demonstrate intimate Fellowship with the Church:
•The word Apostle has also in the New Testament a larger meaning, and denotes some inferior disciples who, under the direction of the Apostles, preached the Gospel, or contributed to its diffusion; thus Barnabas (Acts 14:4, 14), probably Andronicus and Junias (Romans 16:7), Epaphroditus (Philippians 2:25), two unknown Christians who were delegated for the collection in Corinth (2 Corinthians 8:23). We know not why the honourable name of Apostle is not given to such illustrious missionaries as Timothy, Titus, and others who would equally merit it. (newadvent.org/cathen/01626c.htm)
Conversely, what I truly find puzzling is how non-Catholics can claim the right to ordain/commission Priests/Pastors/Bishops when they broke from the Church, with Luther’s schism, and do not share her History nor her Doctrine–yet, they insist on seeking ways to reject the Catholic Church and Sacred Traditions (Oral and Written).