It doesn’t matter if your at your place of work, at home, or in a public space…state laws still apply. For you to see if an employer can record conversations without consent you will have to check and see if you are in a one party or two party consent state.
To put it simply if you are in a one party consent state your employer can record any conversations that they have the permission of at least one person. In a two party consent state it is illegal for your employer to record your conversations without your consent. Telephone monitoring gets a little bit interesting, if you have been directly told that phone calls are for business use only your personal calls may still be monitored.