As was already noted, OP's question about WiFi is ambiguous. WiFi is a casually used term mostly used in relation to router-based networks like in your home or in a restaurant, that allows getting to the internet through the nearby router via wireless (aka WiFi) connection to the router rather than through a wired ethernet cable connection to the router. But this is still for internet access, utilizing the router's IP-assigning capabilty, in this case through a wireless connection to the router.
This is clearly in contrast to your phone always using the wireless cellular LTE network itself for phone calling functions. This same phone company wireless cellular network can also be used to provide internet connectivity to the phone, by making use of the phone company's wireless cell network. Still wireless. But is it called "WiFi"? Very ambiguous words, so you need to be more specific in discussions.
Nevertheless, if the question is about what equipment might be usable IN A HOME WIRELESS ENVIRONMENT, in order to allow much improved wireless connection for portable devices around a large house (to improve internet connectivity wirelessly to the "main router" located in the far reaches of the home), I can highly recommend two retail systems. Both make use of the new "mesh networking" technology that really blankets the home with a strong wireless network.
(1)
Eero, which has three very attractive white modules that can be placed around the house. The "master" must be wired-connected via ethernet cable to either the cable modem's LAN port (if you don't already have a router), or via ethernet cable to a port on your existing router (possibly with its own current wireless network) to create a new second wireless network for your home.
If connected directly to the cable modem the Eero generates its own brand new wireless network in your home, and actually functions as a real wired/wireless router. Each Eero device has two ethernet ports on it so that you can connect to it either via wired or wireless method.
If connected to a port on your router with its own already existing current wireless network, the primary Eero unit must be set to "bridge mode" (i.e. becoming in effect just a "wireless access point (WAP)" for the primary main router, so as not to be a second true router on the network which would produce conflicts. In this more sophisticated setup the main router is still the one-and-only router for the house, controlling all wired and wireless devices connecting to it either directly or through the new Eero-hosted second wireless network. So the house would now see two wireless networks, one from the main router as best as could be seen, and the second from the Eero mesh-network devices and which would no doubt be MUCH STRONGER at distance.
After connecting the first primary device wired to the modem, you place a second device somewhere in the middle of the house. And you configure the software wizard setup to describe generally whether your house is either (a) long and kind of narrow, or (b) more wide and square shaped. The wizard provides placement tests so that you can see if your chosen location for a device is excellent or not.
Once the second device has been properly placed and added to the network you repeat for the third device, at a far location. If the second device was somewhere around the mid-point of the house, the third device is in another room a similar distance away. In this way the three devices provide "blanket coverage" of its wireless network to the entire house, by starting at the primary base station and relaying from one device to the next. Works fabulous.
(2)
Amplifi HD, which is more expensive than Eero.
Same idea, i.e. mesh-network, as Eero, and again three devices in the base package.
More sophisticated router functionality than Eero, and four wired ethernet ports on the "base station" primary unit that again connects wired to the modem via ethernet cable. Again, can alternately be configured to run in "bridge mode" when connected to a port on your primary existing router, in which case its network is a separate second wireless network in your house.
Much larger remote devices which may present problems plugging into wall sockets if you don't have adequate vertical or horizontal clearance. But performs great.
Note that both Eero and Amplifi HD allow adding more than just the base three devices that come in the original package. If your home needs more than three devices to provide proper mesh-coverage, you can buy individual additional units and add them to the network the same way as you did with the originals.