What is the purpose of (native) VLANs and why do I need them?

So far I read this article about VLANs and the article said to watch this PracticalNetworking video regarding the use of native VLANs. Now my question is the following:

I assume I have

3 VLAN capable servers:
• Server A (VLAN 10) IP: 10.0.10.1
• Server B (VLAN 20) IP: 10.0.20.1
• Server C (VLAN 30) IP: 10.0.30.1

2 Switches
Switch A and Switch B
both with a trunk for all 3 VLANs.
The native VLAN is 30

and 3 End-Devices. 2 of them are VLAN capable
• AP A (VLAN 10) IP: 10.0.10.2
• AP B (VLAN 20) IP: 10.0.20.2
• Smartphone (no VLAN) IP: 10.0.30.2

My understand of the native VLAN is, that if my smartphone sends packets out to my switch, the setting for native VLAN automatically makes Switch B assume the packet is meant for the VLAN 30, correct?

Is my example flawed, do I understand something not correctly or am I correct in my assumption?