Pair your phone with a Bluetooth Device (phone, headset, etc.). Try downloading an app on your phone. Uninstall the app. Now try installing the same app with the Bluetooth turned off on both devices, and compare which “installing” was faster. Now, is it with the Bluetooth turned on? Or with it turned off?
Likely, the result is: with Bluetooth turned on, the internet connection is slower. Why is that? Let us first understand what Wi-Fi and Bluetooth are.
Wi-Fi
Wi-Fi allows computers, smartphones, or other devices to connect to the Internet or to communicate with one another wirelessly within particular areas–like our homes, and also in many restaurants, hotels, and malls.
There’s a device from an Internet Service Provider (like PLDT)—a router that can transmit the wireless signal to nearby devices that are connected and that can reach the wireless signal. Or you could simply go to a store to get your phone (with a sim) loaded-up for usage of Mobile Data. You could share your wireless internet connection with others by turning on your Wireless or Mobile Hotspot.
Bluetooth
Bluetooth is a wireless technology whose purpose is to connect gadgets to transfer data without a cable. The Bluetooth module is a tiny part of the chip in a device, which lets it wirelessly communicate with a Bluetooth module on any other devices. Among the various wireless standards (like Wi-Fi), Bluetooth is known for maintaining a stable connection in short distances, and transferring small amounts of data.
Did you know?

Specifically, Bluetooth 4.2 can send data at up to 1 Mbps, which will increase to 2 Mbps with Bluetooth 5. The distance between devices is about 11-16 yards with Bluetooth 4.2, which will go up to 44 yards with Bluetooth 5.
The Interruption
Wi-Fi has a stronger and faster connection; Bluetooth has a stronger but slower data transfer. Bluetooth interferes with the same 2.4 GHz radio waves that Wi-Fi and other wireless radio signals use. The disturbance on your Wi-Fi caused by your turned on Bluetooth, has the same effect like using your microwave oven while using your Wi-Fi. How is this true?

The image above shows what the wireless signal looks like in a person’s suburban home. The diagonal lines represent the Wi-Fi broadcast. There’s not a lot of interference, and you can see his Cisco Aironet 1240 AP (a router) humming along as visualized by the wavy lines in the waterfall spectrogram.
The problem is that both microwave ovens and Wi-Fi operate on the same frequency, 2.4 GHz. In theory, a properly shielded microwave shouldn’t leak any radiation, but the reality is that they leak quite a bit, resulting in electromagnetic, or Radio Frequency Interference (RFI). And yes, Wi-Fi is a radio signal, but it’s broadcasting on a much higher frequency than most broadcast radios operate on. But check out what happens when he turns the microwave oven on:

Whoa—that’s a hot mess all over the RI Spectrum. This image captures 30 seconds worth of data as the microwave warmed a mug of water. You can see through the swamp of RF that the access point does its best to compensate for the signal interference, but that’s a pretty strong blast of RFI.
So in conclusion, Bluetooth interferes with the same 2.4 GHz radio waves that Wi-Fi and other wireless radio signals use–the reason why our Wi-Fi connection gets slower when a device with the Bluetooth turned on is nearby.