Whether it is a potential PhD supervisor, committee member, or employer I think it is important at this stage to simply send a polite kind reminder.
I have been in many of these situations and did not know how to handle it properly. I found it worked best for me to send a reminder 1 week afterwards your conversation; best timing: first thing in the morning, avoid weekends; so you catch his/her attention without pushing/forcing the person. Send two/three reminders max (one per week) if there are answers at that stage drop it.
That would be a short template of this form (short is important there)
I hope you are having a pleasant day.
I was wondering if you had the opportunity to review my email sent out on xx.xx. I know you are particularly busy at the moment but I would be really grateful if you can please spare a few minutes of your time to read it through.
Have a great day ahead.
First name Name
Regarding the formality, it depends, some people like to be called Prof. or Dr., other prefer to be informal after the first contact.
Whenever in doubt, use the polite form.
For the first sentence you can be more specific: winter, summer, vacations, back from a conference, etc.
For the salutation, it will depends on the first exchange of emails, again some people prefer to be more formal other less. You will often find "Best regards" "Sincerely Yours" "Yours sincerely" "Kind regards" "Best" "Cheers" etc
For the signature, also full name (first name + name) or simply your first name.