@anna That is as I expected. Although I hadn't realized that ufw was installed by default. But it does make sense that it is disabled by default.
Ubuntu Touch aims to be a consumer ready mobile OS. Firewall administration is considered an advanced feature, which the typical user is not expected to need to deal with. And even then there would need to be some form of graphical settings page to simplify administration of the firewall at the very least.
Furthermore, it is not really that ports are blocked by default on Ubuntu Touch, rather that there are no services running on the phone by default that are listening on any ports. This is the reason nmap flags the ports as closed.
This is also the reason why it is good practice to only enable ssh temporarily, and also only when your device is connected to a trusted network. In this case having a firewall would not make ssh usage more secure.