Exposing Pi-hole's DNS server via a public IP will turn your Pi-hole into an open resolver, thus posing a potential threat for all Internet users, e.g. by serving as a multiplier in a DNS Amplification attack.
The Pi-hole team strongly discourages Pi-hole’s usage as an open resolver, and we won't provide support in that case.
The recommended way to remotely access a home-based Pi-hole would be to also run a VPN server in your network, exclusively allowing VPN clients via authenticated, secure VPN connections.
Another option would be to run your Pi-hole behind a DNS-over-TLS(853) or DNS-over-HTTPS(443) proxy, where only that proxy would be publically exposed.
Using DoT would also allow you to use certain smartphone's Private DNS feature to connect to your Pi-hole remotely.