If xyz user login and post 10 different ads on different location, different category with every ad different phone number, when we see on category page all ads shown same phone numbers instead of each ad submitted unique phone number.

1 advertiser can submit 100 ads with multiple location, category with different different phone numbers, but when all ads check, most of time many ads shown same number everywhere.

Osclass 8.2.1 - Php 8.2 - Latest epsilon 1.4.8

How to fix this?

Depends if ad shows seller phone or item contact phone.

Item contact phone.

Osclass use this function in loop-single.php:
  $phone_data = eps_get_item_phone();

It will try to get phone in following order:
  $mobile = osc_item_field('s_contact_phone');
  if($mobile == '') { $mobile = eps_item_extra(osc_item_id())['s_phone']; }     
  if($mobile == '' && function_exists('bo_mgr_show_mobile')) { $mobile = bo_mgr_show_mobile(); }
I don't see any issue there.
Maybe osc_item() does not work OK for you, but then it would not even show data from that item.

This issue happen when we edit phone number via admin dashboard item edit form. But when logged as user and then edit item then its work fine.
Test oc-admin dashboard any item edit phone field without logged as user.

Test it and update here. Thanks.

Check what you got in database.