Footnote 30 at Gen 48:16 in the NET Bible, concerning "angel," says (quoted from here):
Smr reads “king” here, but the traditional reading (“angel”) may be maintained. Jacob closely associates God with an angelic protective presence. This does not mean that Jacob viewed his God as a mere angel, but it does suggest that he was aware of an angelic presence sent by God to protect him. Here he so closely associates the two that they become virtually indistinguishable. In this culture messengers typically carried the authority of the one who sent them and could even be addressed as such. Perhaps Jacob thought that the divine blessing would be mediated through this angelic messenger.
Footnote 31, concerning "redeem," but rendered "protect" in the NET, says:
tn The verb גָּאַל (gaʾal) has the basic idea of “protect” as a near relative might do. It is used for buying someone out of bondage, marrying a deceased brother’s widow, paying off debts, avenging the family, and the like. The meanings of “deliver, protect, avenge” are most fitting when God is the subject (see A. R. Johnson, “The Primary Meaning of גאל,” Congress Volume: Copenhagen, 1953 [VTSup], 67-77).
Here is a comparison of how the verse is rendered in various translations. It will give you a sense of how these translators understood the verse.
This portion of Gen (48:9-18) has been proposed as having a chiastic structure. (See here.) In the chiasm, verse 15b and 16 form the pivot (or central) point. If so, then 15b (referring to God) and 16 (referring to the angel) form a sort of parallel idea.
On this page, all of Gen 48:1-22 is arranged into a chiastic structure. But, as you can see, verses 15-16 again form the pivot point. And, as such, the phrase about 'God being his shepherd' and the phrase about 'the angel protecting/redeeming him from evil' would form a parallel idea. Each phrase describing the same thing.
In a sense, Jacob acknowledges God as having 'shepherded' him (Gen 48:15) by means of an angel (Gen 48:16). The idea of 'shepherding' carries with it the implicit idea of 'protection.' Compare Psalm 23:1-4 here.