I CANT LOG IN TO MY FACEBOOK ON MY COMPUTER BECAUSE I LOGGED IN ON MY PHONE BUT LOST MY PHONE

To log into your Facebook account:
1.Make sure no one else if logged into Facebook on your computer/
-To log someone else out, click "down arrow" at the top right of your Facebook homepage and select log out
2.Go to the top of www.facebook.com and enter one of the following:
-Email Address: You can log in with any email address that is currently listed on your Facebook account
-Username: You can also log in with your username
-Phone number: If you have a mobile phone number confirmed on your account you can enter it here (skip the zeros before the country code and any symbols)
3.Enter your password
4.Click login

If you can't log into Facebook and need to reset your password: Go to the login page at www.facebook.com. In the top right, click Forgot your password? Type the email, phone number, full name or username associated with your account, then click Search and follow the on-screen instructions.

Phone Number:
1-650-543-4800
Average Wait: 12 mins
24 hours, 7 days

Log your grandson out by clicking on the log out in the upper right corner. Then go to www.facebook.com and log yourself in with your username and password.

I'd suggest just to reset your password and try again.

Click the little gear icon in the upper-right then click "Log Out."

Please be more specific-Is it on your computer or mobile?which mobile(or mobile os)?
Also try forgot password

Log off Facebook in 2-3 Steps:
1. Click drop down arrow in the top right corner of the screen.2. Select Log Out.
Tip: 3. When logging into Facebook, be sure NOT to check the box titled "Keep me logged in" if you do not want to remain logged in. This box may be checked as a default.
Step 1

Step 2

Tip: Step 3

that problem sounds like your phone. But you can call customer care for att and they will tell you weather you need to replace your phone.