The phrase ‘I hold you in my heart’ is an example of a metaphor. In this expression, the heart is used symbolically to represent love, affection, or deep emotional connection. The speaker is not literally holding someone in their heart, but rather conveying the idea that the person is cherished and loved deeply.
Personification, on the other hand, involves giving human traits or characteristics to non-human entities. In this case, the heart does not exhibit human behavior, but rather serves as a metaphor for the feelings one has towards another person. Thus, while both devices are used in literature to express emotions and ideas creatively, the given phrase is primarily a metaphor.