WASHINGTON - Millions of small businesses and low-income taxpayers will be shortchanged or excluded altogether from a Bush administration tax refund program, according to lawyers who have filed a class-action lawsuit in the controversy. The criticism comes amid a Treasury Department plan in which the public stopped paying a 3 percent federal excise tax on long-distance telephone calls as of July 31. The tax collected by phone service providers had been levied without congressional authorization. The government says taxpayers can get back the last three years of the excise tax payments by asking for the money on their 2006 tax returns. The Treasury Department said recently that $13 billion will be refunded, but it provided no estimates of how much the average phone customer might receive.