Why would this be phishing? The URLs its pointing to is straight on the Coinbase site, over HTTPS too.
https://coinbase.com/transactions/533aa310101a7b619b0001a5How did they sign emails to be as if they were sent from coinbase too?
The only reason this would be actually dangerous is if the coinbase servers themselves were hacked and were storing passwords...
I think it's just an April fool joke by someone taking advantage of the the facebook like module that shows users emails on coinbase.
Not a phishing attempt but it is good to be cautious by never clicking a link in any email you weren't expecting.
Most likely someone who wanted to highlight the problem and convince coinbase to fix it, they have known about this issue but didn't consider it a problem.