Reduce Interference
Wi-Fi signals can be affected by other electronic devices, including cordless phones, computers, microwave ovens, and Bluetooth devices like speakers and headphones.
If you’re unsatisfied with your iPhone’s Wi-Fi signal strength and you’re using it near other devices, moving away or turning them off could make a difference.
This interference also increases the farther you get from your router, partly because the Wi-Fi signal gets weaker but also because your iPhone is more likely to switch over from the fastest, short-range 5 GHz signal to the slower but longer-range 2.4 GHz band, which is closer to the frequency range most other wireless devices in your home operate on.