Parrots will chew on most things, even materials that are harmful to them or valuable to their owners. Parrots enjoy chewing especially during the season when the days begin to get longer (end of winter, early spring in the northern hemisphere). Birds are busy with their beaks all day in the wild. They can become bored if they are not able to move around and explore with their beaks during idle time. 

Within his cage, indestructible perches and toys are cost effective but you should also provide chewable toys and foods for the bird's entertainment. Apples and carrots are fun for birds to destroy while they eat. There are many chew toys and puzzles for birds available from pet stores or catalogs. You can make toys if you keep safety in mind. Natural branches from trees that have not been treated with any pesticides are perfect to use as perches. Offer appropriate toys before they are needed. 

The obvious cure to chewing is to supervise your pet when he is out of his cage. If he is never left alone with access to your valuables, chewing isn't really a problem. While he is out under supervision, and you notice him chewing an inappropriate item, offer something safe to chew. Remember to give birds affection as a reward for playing with toys so that they don't learn to attack your belongings to get attention. Keep his play area and cage out of reach of woodwork and drapes or cords.