When looking for synonyms for the phrase "more difficile," one can consult various sources such as thesauruses or online dictionaries. Some possible options include "more challenging," "more complex," "more demanding," "more intricate," "more arduous," "more difficult," and "more strenuous." Each of these synonyms conveys a similar meaning of increased difficulty, but with slight variations in nuance and tone. For instance, "challenging" may imply a sense of excitement or adventure, while "arduous" suggests hardship or struggle. Ultimately, choosing the most suitable synonym will depend on the context and the desired effect on the reader or listener.