I always thought "Forgive me Father for I have greatly sinned" was the more the traditional phrase you use when you enter the confessional but I've heard others say "Bless me Father" is more traditional.

Neither the council of Trent nor the catechism of st. Pius x list specific required wording,. 

The Baltimore Catechism #427 says, "Bless me, father, for i have sinned..." 

The prodigal son said, "Father, I have sinned against heaven, and before thee, I am not now worthy to be called thy son."

I was taught, "Forgive me, father, for i have sinned..."  it is how I have taught my own children.

This article, while from a modern publication, explains well that it doesn't matter how you begin:
https://www.osvnews.com/amp/2017/10/04/bless-me-father/

Just remember:
To make a good confession five things are necessary: (1) Examination of conscience; (2) Sorrow for having offended God; (3) A resolution of sinning no more; (4) Confession of our sins; (5) Satisfaction or penance

I was taught this way..
"Bless me father for I have sinned, it has been (amount of time) since my last confession and I accuse myself of the following.. (name sins)... For these sins and any that have escaped my memory at this time I asked for pardon and absolution"

Taught by the parish priest at our school in 1965 or 1964.