VOIP security with AVM Fritzbox

[A Former User]

According to the AVM documentation the fritzbox uses the ports 7078-7110 for RTP. I added this NAT Rules:

Forwarding:
Source-IP: Any
Source-Port: Any
Dest-Port: all >1024
NAT-IP: Fritzbox ip
Nat-Port: 7078-7110
Firewall-Filter-Rule: pass

Outbound NAT
Source: Fritzbox ip
All other options wildcard
Static yes

This setup works pretty good, but ist it secure? Can I make additional changes ti improve security?

Thanks