how do i access iCloud.com if my phone is not available

In that case, having more than one trusted device or phone number would be perfect:

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Trusted phone numbers

A trusted phone number is a number that can be used to receive verification codes by text message or automated phone call. You must verify at least one trusted phone number to enroll in two-factor authentication.

You should also consider verifying an additional phone number you can access, such as a home phone, or a number used by a family member or close friend. You can use this number if you temporarily can't access your primary number or your own devices.

Verification codes

A verification code is a temporary code sent to your trusted device or phone number when you sign in to a new device or browser with your Apple ID. You can also get a verification code from Settings on your trusted device.

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What if I can't access a trusted device or didn't receive a verification code?

If you're signing in and don’t have a trusted device handy that can display verification codes, you can have a code sent to your trusted phone number via text message or an automated phone call instead. Click Didn't Get a Code on the sign in screen and choose to send a code to your trusted phone number. You can also get a code directly from Settings on a trusted device. Learn how to get a verification code.

If you use iOS 11.3 or later on your iPhone, you might not need to enter a verification code. In some cases, your trusted phone number can be automatically verified in the background on your iPhone. It’s one less thing to do, and your account is still protected with two-factor authentication.

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copied from: Two-factor authentication for Apple ID - Apple Support

In the discussion as you inquired .

Simple answer to a more complicated problem. Let's imaging one is traveling and one's iPhone is stolen or lost. You arrive at a hotel or a friend's place and use their computer to log into iCloud, but you have no way of authenticating because your "trusted device" is not available. The question is not about how to log into iCloud but getting past authentication. Thank you in advance for considering this problem.

The 2FA account was originally created from an iPhone ( it means it was a single iPhone used and the account is created from the hardware address of iPhone ) , its impossible to sign in with account at www.icloud.com using a web browser .

The account is created from iPhone and not from another Mac in a hotel , or a friends Mac suppose it would have worked , than users if loose their iPhone and they will easily get signed in the account with unknown Macs .

See the articles iCloud security overview - Apple Support

Apple Platform Security - Apple Support

In case if the account was set originally from Mac and you had added a trusted number it could a single iPhone or two in that scenario , the verification could be obtained , by clicking on get verification code , the code is displayed on the Mac screen .

You can use the browser on your computer to log into your iCloud Account.