A debt collector can call you at work but once you tell them not to and you say that your employer either doesn't allow those types of calls or it's inconvenient for you, then it's actually a violation of the consumer protection laws for them to continue to call you. Those laws include the FDCPA, the Fair Debt Collection Practices Act and we have a Florida counterpart called the Florida Collection Practices Act.
Both of those laws prevent calls to work when you've told them not to, so it's important to express that. Perhaps take the date, and time, and the name of the person that you spoke with when you asked them not to call at work and then consult with an attorney about your rights. Most attorneys in these areas represent their clients on a contingency fee basis, which means the cost and the fees of the suit are obtained afterwards from recovery, so there's usually nothing upfront due and there can be statutory damages of $1,000 to you for each violation under those statutes.