The only thing a VPN does is hide your IP address from the website that you are trying to access. It doesn't necessarily offer additional security when browsing the internet at work, the websites are already encrypted and verified with SSL/TLS certificates. There is a lot of confusion out there about VPNs offering more security when accessing a website. Your best security asset is between your ears.
Without VPN:
Phone ---> Hospital Wifi Router ---> Website (Hospital Wifi router sees what website your requested, website sees your IP address, only website sees what you typed and your passwords, login, etc)
With VPN:
Phone ---> VPN encrypts data ---> Hospital Wifi Router ---> VPN server (decrypts only VPN level encryption) ---> Website (Hospital Wifi router sees you using a VPN, website sees VPN server IP address, only website sees what you typed and your passwords, login, etc)
A VPN would allow you to have less concern with a "man-in-the-middle" attack at your site of work as all your web traffic is sent encrypted to the VPN server before being un-encrypted (by the VPN) and sent to the website. But now, you are just trading one risk for another. Am I safer with my work place's internet knowing which websites I visit or the VPN service knowing which websites I visit? Again, neither your work place's IT department nor the VPN service can actually see what you are specifically doing on the websites just that you are accessing them since the vast, vast majority of website utilize "https" and not "http" meaning the page is encrypted and verified. If they can, there is a problem with the encryption algorithm which means that there is a much more systemic problem at bay.
So what should you do? Just turn off the wifi on your phone when you want to do financial stuff at work from your phone. It's basically saying that you are trusting your own phone service provider with knowing that you are accessing financial websites and you don't have to worry about a random VPN service or your work's IT department knowing about it. You also don't raise suspicions with the hospital asking "why are they using a VPN?" or "why are they trading stocks at work?".
So when should you use a VPN? When you want to use fast wifi at the airport, on a plane, in another country, or public wifi hotspot when you don't have phone service or very limited phone service forcing you to use sketchy wifi to accomplish tasks. This shifts the risk from a highly targeted and dangerous access location to a (likely) more secure and reliable VPN service.
What VPN to use? I recommend ProtonVPN. It's free, reliable, decently fast speeds and it comes from a trusted company. Yes, VPN inherently burns more battery, uses more CPU, and will likely slow down internet speeds since there is a lot of work being down on the back-end.