You shouldn’t expect to be invulnerable to advanced malware like Pegasus simply by choosing the right phone, however more secure phones (such as a new Google Pixel running GrapheneOS or a new iPhone in Lockdown Mode) can be more difficult/expensive to attack.
The Google Pixel is the only recommended phone (and is currently the only device supported by GrapheneOS) because it is currently the most secure Android device around. Apparently Google Pixels running GrapheneOS have been the most resistant to Cellebrite exploitation.
If for whatever reason a Pixel or iPhone is not an option for you, Samsung is probably the next best thing. They aren’t privacy friendly but they offer the longest security update support periods and it seems to be the opinion of many that they’re essentially in third place when it comes to security features.