Assuming you are syncing all your contacts with Google Contacts: The web app it can/will fix/merge the duplicates for you, too (see pic below).
Also, make sure you're not (inadvertently) storying contacts in multiple places. When you add a contact on the phone, it can store it locally or in any contact list you are syncing with (e.g., Google Contacts). You can actually be syncing with multiple external contact lists (e.g., Google, Microsoft, Yahoo, etc.), also adding some locally ONLY, that can create a mess.
Choose ONE place to keep/sync all your contacts to avoid the mess that gets created by storing them in multiple places AND syncing to an external location.
If you're going to get a new phone, then just disable syncing your contacts with your old phone, go clean it up on the web, then set up your new phone to sync.
- OR -
If you want to give it a whirl and try to keep the old phone, disable syncing your contacts, back up anything on the phone you want to keep (if not already doing that), reset/wipe the old phone (factory reset), and only AFTER you go on the web and clean up your Google contacts, enable syncing your contacts/calender/etc.
Personally, the only Google app I use is the Contact list (I do not use Gmail, Calendar, Drive, Photos, etc.), and that's where I sync all my devices to. All contacts go in there and are synced - none are stored locally on the device(s). I use Dropbox (paid) and have my phone set to upload every picture taken (instantly). Finally, I use Fastmail (paid) so all mail is stored/accessed in the cloud and, if a device is syncing, it uses IMAP and not POP3 (IMAP leaves it in the cloud while POP3 downloads it to the device and removes from the cloud, if so configured). Sure, you can do the same with your email and pics with free accounts like Google, Microsoft, Yahoo, etc., but I avoid the free solutions for a wide variety of reason, mostly involving security, reliability, storage limitations, and privacy.
The reason I do what I do is that I can literally replace my phone (lost, stolen, or if I just decide to reset the phone to factory settings and start over), nothing is lost, and I'm back to 100% in mere minutes with almost zero effort. Nearly 500 contacts are added in seconds, my email is untouched, and all the photos that were on the old device were already synced to Dropbox in real time. All is accessible on the web, too. All I have to do is re-add my apps (easy from the Google Play Store list), as I always take the opportunity of a new phone to only re-install the apps I'm really using and weed out the crap that I installed since the last time I refreshed.
Oh, if you use a MFA application, I strongly suggest using Authy AND having more than one device associated with your account -- by far the easiest way to add/re-add your lost/replaced device as an MFA device versus other MFA solutions.
View attachment 409607