Mri:mild bilateral cerebellar tonsilar ectopia at the level of the foramen magnum borderline phenomenon. what does that mean. pls explain thanks. ?

Usually not much: This usually means that a small part of the back portion of the brain (cerebellar tonsils) descends into the spinal canal very minimally. Usually this is incidental, and nothing needs to be done about it. However, not a bad idea to meet with your primary care doctor and discuss it and be examined in the context of this finding.