If your brother holds a valid power of attorney, then he is the one legally responsible for making the decisions--and the nursing home personnel will be required to do his
Is there any way you get to the bottom of why your brother seems unwilling or unable to communicate with both the folks at the nursing home and with you? Try approaching him in a spirit of cooperation--emphasizing that you both want what's best for your mother and that you are willing to help in whatever way you can.
Perhaps he needs a dedicated cell phone so that he can be reached more easily. He may also be willing to give you brief regular updates by phone or email if you emphasize how important it is to you. Or perhaps he feels busy with work and family matters, or is finding out that he is not emotionally equipped to take on the job of attorney-in-fact for your mother--and would actually be relieved to have someone lighten the burden.
You might contact the ombudsperson at the nursing home and present your concerns; he or she may have dealt directly with your brother and may have the best idea of what the sticking points have been in the past.
If this informal approach doesn't work, you may want to consider going to court to have your brother removed as the attorney-in-fact. This is a rather drastic step, and would require that you have strong evidence that your brother was not acting competently and diligently. The person named to act as successor would then take over if your mother named one in the original power of attorney document. If no successor was named, you would need to request that a conservator be named to make financial and health care decisions for your mother. You would most likely need to hire an attorney for help to accomplish these legal tactics.