Yamaha YPT 310 - I'm trying to hook them up with my headphones (Astro A40's)

I'm wondering if it is even possible to hook my old YPT 310 with my headphones, which are your generic AUX cable headphones. I've looked up in the YPT Owner's manual but it provides very very limited information about how to actually do so (it basically just says to plug them in). However, the phone/output port on the back of the keyboard (where it says to plug in the AUX cable), is way too small for any the aux cables that I have. The ones that came with my Astro's will get stuck in the slot before they get all the way in.

(This one that I got from amazon is too small as well https://www.amazon.com/Anker-Premium-Auxiliary-Headphones-iPhones/dp/B00R124LAK). Unless I am mistaken, my Astro's AUX is a 2.5mm cable while the amazon one I linked is a 3.5mm

I've also mistakenly bought a MIDI 5pin to AUX converter but that hasn't bore any fruit either. Any help would be appreciated!