I purchased bitcoin through a bitcoin ATM, and I opened a new wallet on the spot.
On getting home my phone was mysteriously wiped, how can I find the wallet I created? I happened to write down the 12-word phrase.
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It is good you wrote down the 12-word seed phrase. Without that, you bitcoin may have been lost forever! Do not share that phrase with anyone, no matter what! If you do, they will be able to easily steal your bitcoin.
You can use that 12-word phrase to recreate your wallet on another device. It sounds like what you have is likely a BIP39 mnemonic seed phrase, so you'll need a wallet which accepts a 12-word BIP39 seed phrase.
You can use a website like btcinformation.org to browse available wallet software. It is important to do your research and choose a wallet that is legit, look for many independent reviews of the wallet if you can.
Once you have the wallet software running, you should see a prompt to either start a new wallet, or recover an existing wallet. Choose the recovery option, and follow the steps to input your 12-word seed phrase. Doing so should recover your wallet, and once the software is synced you should see your bitcoin balance again.
I happened to write down the 12-word phrase.
You are in a very good situation. Much better than many new bitcoin owners who ask questions here. It is very likely that your bitcoin is safe and needs no urgent action.
how can I find the wallet I created?
You don't need to, wallets are not important so long as you have the 12-word seed-phrase. Wallets don't contain your bitcoin, they are just a way of using the private-key (derived from the seed-phrase) which gives you control over your bitcoin.
Wallets are completely disposable. Just keep backups of your seed-phrase (or the private key itself) and guard them very closely.
The key things to do are
How can I recover from a 12 word seed phrase?
Chytrik's answer give you some good advice. The exact steps depend on which wallet you decide is best for you.
If you want to hang on to your Bitcoin for five years, you need do nothing other than lock away in a very safe place your 12-word seed-phrase.
I understand you'll feel compelled to check the amount of bitcoin you control though, that involves at least using a wallet to derive the private key from the pass-phrase and to derive the receiving address from the private key. The wallet will do all this automatically when you import the seed-phrase into it. Once you have an address you can check the unspent bitcoin value associated with that address by using any of several blockchain explorer websites.
Useful references here