You can specify the order in which Providers appear on the appointments page.

From the Appointments screen got to Setup >> Provider Sort Order

You will be asked 'Do you want to set a sort order for you only?

If you wish to only change the sort order for this user Click Yes or click No to change the order for all users.

This will present you with a list of the providers. You can choose to sort them based on Time, Name or None.

If creating your own custom sort order choose None then select a provider and use the up and down arrows to move them either up or down the order list.

Once all providers are in order choose OK to complete.