I applied for PIP, and got a text saying I have to speak to them on the 22nd. Is it an interview?

I was led to believe that because of the pandemic there are no face to face assessments going on at this moment in time but there are telephone assessments where you get the opportunity to tell them more about your disability. They have set questions and you need to answer them truthfully and say if anything has altered . 

I would suggest you make a diary now so you can state facts for example on Wednesday the ...I could not leave the house due to my breathlessness and this has been a increasing pattern for my COPD . The same applies to chronic pain or for your mobility they will ask how far you can walk . 

Can I stress please state your worst day as this is not a martyrs situation , none of us like to admit how bad we are or all of the things that now become a issue . If you say oh I can do this that and the other you will be down graded . 

The way you answer your. Questions needs to be the same as you replied on your application unless your condition has deteriorated. 

Mention if you need a advocate with you for support . Unfortunately sometimes my brain is so foggy I can’t think and it is useful to have a advocate this in no way makes you look stupid . It is helpful as they can prompt you when you have missed something out or actually talk on your behalf if maybe you are breathless .
unfortunately we all have to go through this process but it is well worth it .
Stress is also part of the assessment now and is considered for PIP .
Also benefits are paid from the date you applied or if my memory serves me well 6 months before your claim if you had the condition that you are claiming for once that has been processed there is a set period of time you will be informed of the decision, and if you disagree with this decision you can appeal and once again have a advocate with you , this can be family, friend or their are advocacy groups in area which can come with you to a tribunal . Citizens advice are always a good place to tap in for networking.
It is much better if you can get someone to help you fill out these forms as they know the key words the benefits agency is looking for . Even I do that as it gives more clout to your application! 
I forgot to say the benefit will be paid from the day you were entitled to it .
I hope that you have found this helpful ?! 

I wish you every success in your application and anyone else who finds themselves in the same position.