When accusing an attorney of charging excessive fees, what could constitute as excessive? Ex: "telephone conference with voicemail".

Your example does suggest overreaching by the billing attorney.  Negotiating a reasonable billing may be your best approach.  Using the hourly rate provided in your written fee agreement, and the bill presented by the attorney to identify actual hours of productive work to calculate the resulting fee.  Pay that amount with a cover letter explaining the basis for your payment amount.  If your attorney continues to assert a claim for the total inflated billing, you respond that you believe the billing is excessive to the point of violating the rules of professional conduct.  You may then consider either a legal malpractice claim or a grievance with the Colorado Supreme Court disciplinary council.