How many warnings were you given prior to suspension?
Usually, you are spoken to maybe 1-2 times before a written warning. At least that's how it is at my store. Each manager is different.
You're not supposed to be on your cell phone at work. Were you on the phone? The only time it may be ok is if you are helping a customer that is not cell phone savvy.
As for your next step: don't commit time theft or anything that can be construed as time theft
