Hello apurva

I hope you are doing good  . I would like to help you by awaring you in google photos, photos are generally synced to your gmail account . Make sure when you logged in your google account you are using the same gmail id which you haved used in your old phone .  I would also like to tell you that now google photos has also sets its limit to 15gb beyond you have to buy space for the backup, this might be the reason for your photos . Moreover, you can look for google drive , drive also automatically stores photos from your phone as backup .

Hope you found this answer helpful. Good luck for your future