A phishing attack is where someone hosts a fraudulent copy of another website for the explicit purpose of collecting personal information from unwitting users (e.g., banking information, social security numbers, usernames and passwords, etc.). I'm fairly certain hosting providers have a legal liability to disable such websites within a number of hours, but of course I'm not a lawyer.
It sounds like you were exploited by a weakness in a PHP application hosted on your server. The attacker used the weakness to upload the phishing website which was later reported to your hosting provider (the owner of the IP space). They investigated and confirmed the activity and shut you down. (I expect.)
You will need to lean on them to provide you additional support. Only they have the power to enable your server, so you should contact them and ask how to proceed. They'll have you remove the questionable material and then I'd imagine they'll leave you to your own devices, but you should probably update any PHP scripts on your system and perform some sort of security audit. I see people here contracting third parties to do them for fairly cheap, so you should look into that option.
You will probably need to have them fix the folder permissions before they will unsuspend your website.
As Anonymous Coward said it's probably due to a hole in the PHP software and if the folder was set to 777 then the files can be uploaded through PHP. I would recommend avoiding 777 permissions as much as possible due to risks such as this which result in the suspension of your site.
Due to the fact that phishing is highly illegal I'm sure your host had no choice but to suspend the account as it can be very hard to dictate that sort of situation.
Wordpress got security holes most likely that's the reason why somebody got into your server.Your hostingprovider is legally requirerd to shut things like this down however contact there support and they will assist you in getting back online.
I recommend subscriding to the maillists of every script(s) you use why ? because you are then notified when a security update becomes availible.Also what php version do you use ? anything lower then 4.4.4 have holes ...