Instagram lets you sign up with an email address, but in practice almost every fresh account is asked to confirm a phone number — either at registration or at the first «suspicious activity» checkpoint a few hours later. A virtual number from Get-SMS receives that 6-digit SMS code, so your personal number stays out of Meta's database and one number doesn't chain all your accounts together.
What matters with Instagram is not the number itself but everything around the signup: fresh accounts registered through VPNs, on «noisy» IP ranges, or immediately mass-following people get flagged regardless of what phone confirmed them. The number passes verification — keeping the account alive is about behaviour.
Register from a clean residential IP, fill the profile (photo, bio) before any activity, and let the account age for a couple of days. If Instagram shows «we couldn't send SMS to this number» or rejects the code, cancel the number free of charge and take one from another country — the USA, Australia, Finland and Poland pools historically verify most smoothly. If the account later hits a re-verification checkpoint, any number can receive the new code — it doesn't have to be the original one, as long as no other account is currently linked to it.
For business profiles and creator accounts the phone plays one more role: Meta Business Suite occasionally asks for SMS re-confirmation when you connect an ad account or change payout details. If that's your use case, a 30-day rented number is the safer choice — you keep receiving codes on the same number for the whole setup period.