If you’re locked out of your Steam account because you set up the mobile authenticator but no longer have access to the phone (and didn’t set a phone number), here’s what you can do—unfortunately there’s no simple one-button fix, but recovery is possible if you can prove ownership of the account.

✅ What you can try

Go to Steam’s Help page: “Help – I can’t sign in”.
Steam Community
help.steampowered.com

Choose the option that says something like: “I deleted or lost my Steam Guard Mobile Authenticator”.
Steam Community

Enter your account name, or the email address you used.
Steam Community

Steam will ask for verification. Normally, if you still have the phone number tied to the account, you can receive an SMS. If you don’t have access to that phone number (which is your case): choose “I no longer have access to this phone number”.
Steam Community

If email is still accessible, they may send a code there. If you also don’t have access to the email, you’ll be taken to a stage where you need to provide proof of account ownership.
Steam Community

⚠️ What you need for proof of ownership

Steam states you’ll need to prove the account is yours. That can typically include:

Payment methods used on the account (credit/debit card, PayPal)

Retail CD-keys of games redeemed to that account
Arqade

Any other purchase information tied to the account.
You’ll also need to supply a reachable contact email (even a different one) so Steam Support can respond.
Steam Community

🕒 Tips and cautions

Be patient: once you submit your support ticket, it may take a while for Steam to respond.

Be honest and clear in your support submission; indicate exactly what changed (phone changed, no number added, can’t access codes).

If you still have any device logged in to that account (e.g., Steam client on PC where you’re already logged in), you might have extra leverage or recovery options.

Going forward: once you regain access, add a phone number onto the account and keep your recovery codes/backups in a safe place. That will prevent this kind of lock-out.

Thank you for the comprehensive reply. Have tried some of things already with no luck, I’ll try the others