You say the chart is not about teaching symbols, but still the learners are seeing them all the time. And I myself panic when I see the symbols.So what is the purpose of having the symbols there? Could you say more about that?
Ok, well, think about this: Instead of phoneme symbols you could put pictures or colours in the squares if you wanted. Or just leave the boxes empty, which I sometimes do. But whichever you do, the students are still learning sounds and not pictures of colours or empty spaces. The chart is not about teaching symbols. It’s about the physicality which produces the sounds.
The chart gives an anchor for each sound
The point is that students are learning muscular movements and connecting that with the acoustic consequence made by each tiny muscular adjustment. The chart gives a location for each sound, and that space is always dependable and never moves. The space is the anchor for that physical / acoustic connection. It enables learners to keep track of the sounds and to discriminate them ever more finely. Again, the priority of the chart is not about teaching symbols. That comes gradually as an added benefit
I don’t ask students to memorise symbols
However, I chose to put symbols in the boxes as these have a later use. Symbols open up access to pronunciation in dictionaries, online searches, in Wiikipedia, and in the students own written vocabulary notes. I never ask students to memorise the symbols. But once they are used to pointing out words on the chart and writing the normal spelling on the board, I may then say to one of them “OK now can you also write those symbols that you have just pointed at?” And she can look at the chart and copy them on the board, So she writes the normal spelling and the phoneme symbols on the board, and begins the process of mastery of the symbols. But I only do this as they are ready. There is no hurry, and this is a side benefit, not the main purpose.
It’s easier to name something you know
Once you have a sound, it is easy to give it a name (in this case a visual symbol). But if you don’t know the sound it is very puzzling to give it a name. For example, your new class of 20 students presents 20 new names that tax your memory at first. You can’t really learn the names until you know the people that the names represent. It’s same with the sounds. As you get to know a sound, then giving it a name (or a symbol) becomes natural and easy. The problem arises when you try to memorise a name without knowing the student, or a symbol without knowing the sound.
Our training teaches us ABOUT pron
Our methodology does not really take teachers into their own mouths to see what is going on and to learn pron from the inside. Rather we learn about pron from the outside, through cognitive models, intellectual descriptions, diagrams and Greek words. This has a role, but the thing that really makes the difference is direct internal connection with the muscles that are being asked to make new movements. For more on the practical aspects see my post Proprioception and Pronunciation
Focus on the physicality not the symbol
So I suggest that you don’t teach the symbols or try to them or memorise them yourself. Don’t emphasise them. Instead prioritise the exploration of the physical postures and movements in the mouth, and the different sounds (acoustic consequences) these postures make. This physical/acoustic experience is then allocated a box on the chart which will always represent that sound. Soon the chart becomes the whiteboard for sounds and words. And since each box contains a symbol you and your students will gradually get used to seeing it, and will internalise the symbol as way of representing that sound. This is not an intellectual or conceptual system. It works by direct connection in the brain with muscle movement and the resulting heard sound.
In summary, I suggest you prioritise what you feel in the muscles around your mouth, rather than the symbols you see with your eyes. And help yourself and your learner to let go of the visual priority of the symbols, and to inhabit the more important priority of the muscles that are being asked to do some new work. As I say, the chart is not about teaching symbols – even though it is covered with symbols!