This is a tad pricey at $40 but it might do just what you need. https://www.amazon.com/Travelon-Anti-theft-Lockdown-Bag-Medium/dp/B078Y3579R
You could wrap the cord around your waist and then lock the bag tight so that no one can steal it from you without you waking up. This would of course only be big enough for your phone and important stuff like your papers that you absolutely cant have stolen.
Also before putting those items in the bag I would put them in a freezer lock bag as Michele has suggested and you can wrap the phone in a tee shirt or two for added protection from being crushed.
for the duffel bag you could use a bike lock and loop it through the metal part that the straps connect to and then run it through the cable on the anti theft bag before locking it so that both the anti theft bag and the duffel bag are locked together.