The problem, however, is that the phrase "personal relationship" is found nowhere in the Bible.
Nowhere in the Hebrew scriptures, nowhere in the New Testament. Jesus never used the phrase. Paul didn't use it. Nor did Peter, James, or the woman (???) who wrote the letter to the Hebrews.
So if that's it,
if that's the point of it all,
if that's the ticket,
the one unavoidable reality,
the heart of the Christian faith,
why is it that no one used the phrase until the last
hundred years or so? (Question marks mine, JK)
Well, it brings to mind the fact that the term, "Trinity" is not in the Bible either, but that does not make it any less true. The Trinity is a true fact and a doctrine of the Christian faith, whether it is referred to by name or not. The same goes for a personal relationship with God through Jesus Christ. Whether people in the past have called it that, that is what it is.
Consider the following (and there are many more);
Now this is eternal life: that they know you, the only true God, and Jesus Christ, whom you have sent. (John 17:3)
...to all who did receive him, to those who believed in his name, he gave the right to become children of God— children born not of natural descent, nor of human decision or a husband’s will, but born of God. (John 1:12-13)
...the Spirit you received brought about your adoption to sonship. And by him we cry, “Abba, Father.” (Romans 8:15b)
Because you are his sons, God sent the Spirit of his Son into our hearts, the Spirit who calls out, “Abba, Father.” (Galatians 4:6)
For those who are led by the Spirit of God are the children of God. (Romans 8:14)
The Spirit himself testifies with our spirit that we are God’s children.(v16)
The relationship sounds personal to me. The relationship between children and their Father is personal, and those who have it, know it.