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Hi MinhP, did you try the suggestions in my previous response, if so could you let me know if your PI can access the internet when a network cable is attached and and wifi is off.

When the Pi is in hotspot mode internet is only available if a network cable is attached to the Pi, can you confirm this your setup when the iphone says no internet

There can be different reasons depending what you pi is and is not doing so can you give me some feedback on the state of your pi.
If Internet via a network cable works fine then we know the pi is working fine.
Have you set your localisation settings in Pi_Configuration for your country, that can cause some connection issues with phones.
On the pi goto Preferences/Raspberry Pi Configuration. Then the Localisation tab and "Set wifi Country"
choose the correct details for your country.

On Android Phones you can't connect to the hotspot of you have Mobile Data active. I don't know about Iphones but try turning off Mobile Data before connection to the hotspot.

If you can let me know the the answers to the above I can look into the issue further, thanks