Lost phone: what to do
What to do, in order: locate it and use lost mode, block the SIM, close banking and email, restore two-factor, file a report and recover on a new device.

[ ] Call the phone and message it
    Sometimes it is with the person at the next table or in a taxi. Start here; it takes a minute.
[ ] Locate it through the find-my-device service
    From a computer or someone else's phone. The service shows the location and lets you play a sound and lock the device.
[ ] Turn on lost mode with a contact on screen
    The device locks and whoever finds it sees where to call. This works more often than people expect.
[ ] Block the SIM with your operator
    While the SIM is active, someone else receives your SMS codes and can call at your expense. This is the first security step.
[ ] Close access to banking apps
    Through another device, online banking or the hotline. Tell the bank the phone is lost.
[ ] Change your email password first
    Email is the key to every other account. After changing it, end all active sessions.
[ ] End sessions in messengers and social apps
    Every service has a device list. Remove the lost one and check for unfamiliar entries.
[ ] Restore two-factor authentication
    Backup codes, a second device or a support request. This is the slowest part; start it immediately.
[ ] Tell work if the phone held work access
    Email, chats, VPN, two-factor. The sooner you say, the sooner access is revoked — this is about security, not blame.
[ ] File a police report with the IMEI
    Needed for insurance, sometimes for the operator, and in case the device is used for something illegal.
[ ] Check your insurance and what it covers
    Sometimes the phone is covered by a card, bank or separate policy. Claim windows are usually short.
[ ] Wipe the device remotely if recovery is unlikely
    After a wipe the location usually stops updating, so this is a last resort rather than a first step.
[ ] Restore your data from a backup
    Check the backup is recent and restore it to the new device. You will also see what it was missing.
[ ] Get a replacement SIM with the same number
    The number is tied to dozens of services, so keeping it matters more than speed. Ask the operator about the process and documents.
[ ] Check accounts for suspicious activity
    Logins, transfers, sent messages, changed recovery settings. Especially in email and banking.
[ ] Set up protection for next time
    Find-my-device on, backups running, backup codes stored separately, IMEI and a photo of the box saved.

Checklist from Unload: https://unloads.me/c/lost-phone