Can the Canon 6D connect to a phone's WIFI hotspot and talk to the Canon app on that phone?

No. In order to use the Canon app on the phone to control the camera, use the phone to see any images stored in the camera, or transfer images from the camera to the phone the phone must connect to either:

• the network created by the camera

or

• a third device providing LAN access to both the phone and the camera.

To share images on social network sites or anywhere else in the web via apps on the phone, you need to first transfer the images to the phone, then

• leave the camera's network and reconnect to the internet via your phone

or

• Use the LAN connection via the third device to upload the images via the apps on the phone.

You can use the Canon Camera app that connects the camera and phone to queue your selected images already stored on the phone to a specific app, like Instagram. You can even select filters, etc. from the Instagram app on your phone while connected to the camera via the camera's network. But when the IG app tries to upload them to the web while still connected to the camera's network it will fail. They'll stay queued, though, and once you reconnect the phone to the web they can be uploaded.

Here's an article that covers it in more depth: How to Share Images on Social Media with Canon 6D Wifi. It is part of a series of articles by the same author covering several different aspects of using WiFi with the 6D. The base article is here.

You can use the camera itself to connect directly via WiFi to a LAN with internet access and upload images directly from the camera, but you won't be able to use the phone's interface, or any apps your phone uses, to do this if you are also using the same phone's hotspot as the LAN to which the camera is connected in infrastructure mode.

In order to use the phone to control the camera or view/transfer images from the camera to the phone, this choice must be selected in the camera's 'Wi-Fi function' menu:

In order to upload images from the camera directly to the web, this choice must be selected in the camera's 'Wi-Fi function' menu:

Both choices can not be selected simultaneously.

It's unclear from the EOS 6D WiFi Instruction Manual if any web services besides the four shown in the screen samples ('CANON iMAGE GATEWAY', 'facebook', 'Twitter', and 'YouTube') can be added to the camera's menu or not. The account settings for those four web services need to be setup in advance using EOS Utility while the camera is connected via wired USB connection to a computer.

(Note: The WiFi setting must be set to disabled to connect the camera to a computer via a wired connection, or to shoot video with the camera. If you don't want to dig into the [Settings (yellow wrench) tab 3] menu to turn WiFi on and off each time, you can include that setting item on the list for the 'My Menu' tab.)