Open WhatsApp on the old phone
Go to Settings
Tap Chats
Tap Chat backup
Back up your chats to Google Drive or iCloud
Install WhatsApp on the new phone
Open WhatsApp and verify the same phone number
Restore the backup when prompted
Wait for the chats and media to finish restoring
If needed, use WhatsApp’s transfer chats feature from the old phone to the new phone
Keep both phones connected to Wi-Fi and powered on during transfer