To use bitcoin then an internet connection is a must, don't you know that basic? Bitcoin is a digital currency in the first place.
To send and receive requires internet. Hardware wallets do not connect to the internet, but they can connect to a computer via USB and the computer can connect to the internet. The user's private keys never leave the hardware wallet; the hardware wallet can generate receiving addresses and sign send transactions. With a smartphone, the device storing private keys is directly connected to the internet, even if only temporarily.
In other words no matter what type of wallet you use you still need internet connection, the phone is not just safer and secure but also more easier to operate because you just turn it on including you can choose to turn your internet conenction on and off whenever you want, if hardware is used then you have to usb cable and other stuff that is more harder than using phone.