Need help recovering Notes (linked to yahoo) that disappeared but are sitll on one iphone offlined

Hi

I have over 600 notes with graphics that magically disappeared from my iMac last week, i tried looking in the gmail account over chrome but they where not there or in the trash,

i then noticed them still on one of our older iphones i recently changed the password for my gmail account which went offline on the iphone, i want to know how i can back them up or restore them..

Thanks