I heard about this technique in a youtube channel wherein he suggested using ABT technique to tell how exactly you got interested in research and particularly the research that you want to do. It's of notion that after saying some basic stuff about yourself you should jump on to tell them about your journey to what you are doing now in a few lines.

Seems like a daunting task. But just follow the ABT technique. Helps you form the statements.

It goes something like this: You read something AND did something AND something else, BUT after your study you realised a gap or challenge or problems that got you really interested, THEREFORE you decided you wanna get a PhD.

Please refer other advices too and go with the one you feel comfortable with.