Because of two factor identification, you CAN'T log onto your iCloud account if you don't have your phone!
How can I find a lost iPhone when all the instructions to find it entail having the phone?!
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You can use any internet browser and log into www.icloud.com/find without being asked for a two-factor code. This is recommended as the first option of step 1 of the instructions in If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support
You can also log into www.icloud.com (without the /find), ignore the code request and click the Quick Access to Find My button instead.
In spite of the above, I would strongly encourage you to set up multiple trusted phone numbers after you have full access. They can be Androids, landlines, friends' or relatives' phones. See: Two-factor authentication for Apple ID - Apple Support