Are there any devices to increase the range of a WiFi network

Are there any methods, specific plates or materials which can boost the signal?

You're likely to succeed only to degrade the signal or its strength - fine-tuning radio transmission requires special equipment and intimate knowledge (as in schematics and calculations) of the actual gear used.

There is no "magic" tin-foil trick that can be used. If your device has a connector for an external antenna that is your only option - but may well turn out to be of little gain, depending on the antenna you choose.

The actual construction of the walls may be relevant; i.e. if there is a lot of iron bars inside concrete walls, or if there is sun-protection film on sheets of glass... - these would attenuate any radio signals.

Note: there are WiFi devices that operate at 5GHz - as these are quite new, you might get less disturbance (few neighbours have them) on such a device - the reach might not be as long though; higher base frequency also implies less reach.

Get a WiFi extender or a client bridge device (something that can connect to WiFi and allows connections via an ethernet port), and connect it to your phone's hotspot.

Then, disable the access point (repeating/extending function) on the WiFi extender and plug an ethernet cable from a LAN port on the extender to the WAN port of a router.

You can usually find old routers on Craigslist for about $15 to $25. Connect all your devices to the access point broadcasted from the router, and that should do. The router, is given one IP, and then splits it up for other devices.

WiFi extenders do not have routing functionality. The reason for this, is because it would be more expensive to build it that way, and... Traditionally it would cause less issues because it connects to one LAN network pool. Aka, the devices on the main access point can still initiate connections with devices connected to the repeater.