There are several synonyms that can be used in place of the phrase "anxious concern." One possible option is "nervous worry," which conveys a similar sense of unease and apprehension. Another alternative is "fretful distress," which suggests a more persistent state of anxiety that may manifest in physical symptoms like restlessness or agitation. "Apprehensive unease" is another possible synonym, conveying a sense of uncertainty or fear regarding a particular situation or outcome. Ultimately, the choice of synonym will depend on the context in which the phrase is being used and the specific shades of meaning that the writer wishes to convey.