Answer:
Face-to-face
Step-by-step explanation:
The team member isn't doing their part and it's affecting the others. This means that the issue must be handled appropriately.
If you used an email, then the unhappy team member would feel as if you're not taking things seriously and are just being lazy.
Texting is even worse, so you wouldn't pick that one as that's more informal.
Using a phone call isn't as bad, however it would still be ineffective as the lazy team member may not pick up, be angry over the phone at a supposed 'accusation' or they'd just make excuses.
Face-to-face is best as you can pick up on body language and visual cues as well as their voice, plus it would indicate to your team members that you take their requests seriously and will act accordingly. This puts you in a great leadership position as it shows confidence, maturity and strong leadership qualities.