How was my account compromised?

This isn't the normal 'my account was hacked' post. Just seeking a better understanding of how my account was compromised.

At noon today I bought $700 worth of coins, 2 hours later they had been transfered out. I verified my account 2 days earlier. I did all of this on my phone. I DID NOT have 2fa enabled which I know makes it my bad. I also noticed that a number of coinbase emails had been moved to my emails deleted folder, though not the ones notifying me of the withdrawls.

Any insight into how this was done would be appreciated so I can help reduce the risk of this happening again. I have already changed my passwords on all my accounts.

Thanks